Air-conditioning apparatus as typified by multi-air conditioners for buildings each include a refrigerant circuit (refrigeration cycle) in which a plurality of indoor units to be independently operated are connected parallel to an outdoor unit (heat source unit). In general, such air-conditioning apparatus each include a four-way valve or other components to be used for switching passages in the refrigerant circuit, thereby being capable of performing a cooling operation and a heating operation. The indoor units each include an indoor heat exchanger (use-side heat exchanger) for exchanging heat between refrigerant flowing through the refrigerant circuit and indoor air, and the outdoor unit includes an outdoor heat exchanger (heat source-side heat exchanger) for exchanging heat between the refrigerant flowing through the refrigerant circuit and outside air. When the cooling operation is performed, the outdoor heat exchanger functions as a condenser, whereas the indoor heat exchanger functions as an evaporator. Meanwhile, when the heating operation is performed, the indoor heat exchanger functions as the condenser, whereas the outdoor heat exchanger functions as the evaporator. Hitherto, in the heat exchanger functioning as the condenser, liquid-phase portions (portions where condensed liquid-phase refrigerant is subcooled) are provided in downstream portions in each of refrigerant paths so that a necessary liquid temperature (necessary enthalpy) is secured in merging portions where flows of the liquid-phase refrigerant flowing out of each of the refrigerant paths are merged with each other.
Further, as heat transfer tubes of the heat exchanger, flat tubes may be used. The flat tubes are higher in heat transfer efficiency than circular tubes, and can be mounted to the heat exchanger at high density. However, internal passages of the flat tubes are capillaries, and hence refrigerant frictional pressure loss is increased particularly when the heat exchanger is used as the evaporator. As a measure to avoid this pressure loss, the number of refrigerant paths to be arranged parallel to each other is set larger in the heat exchanger using the flat tubes than in a heat exchanger using circular tubes.